President Donald Trump told military commanders on Tuesday that troops deployed to “dangerous” American cities should use such locations as “training grounds.”

Trump, during an address to dozens of top-ranking generals and admirals held at the Marine Corps University in Quantico, Virginia, on Tuesday, said they could be called upon to assist in the ongoing federal crackdown on Democrat-led cities over crime and immigration.

The president previously announced that National Guard troops will be deployed to Portland, Oregon, “authorizing Full Force, if necessary,” in a social media post. He also announced the upcoming deployment of troops to Memphis, Tennessee, and to Chicago, Illinois, having previously ordered troops on the ground in Los Angeles, California, and Washington, D.C.

They’re very unsafe places, and we’re going to straighten them out one by one,” Trump said. “And this is going to be a major part for some of the people in this room. That’s a war, too. It’s a war from within.”

He added, “We should use some of these dangerous cities as training grounds for our military — National Guard, but our military because we’re going into Chicago very soon. That’s a big city with an incompetent governor.”

Trump went on to say, “America is under invasion from within. We’re under invasion from within. No different than a foreign enemy but more difficult in many ways because [these enemies] don’t wear uniforms.”